Screener



April 1963 A. R. FORSBERG 3,087,617

SCREENER Filed March 2, 1960 3 Sheets-Sheet 1 April 30, 1963 A. R.FORSBERG 3,087,617

SCREENER Filed March 2, 1960 3 Sheets-Sheet 2 flTTOR/VEYS 4271/02 1?.FORSBERG April 30, 1963" A. R. FORSBERG SCREENER s Sheets-Sheet 5 FiledMarch 2, 1960 Afro/P215);

United States Patent 3,tl87,617 SCREENER Arthur R. Forsberg, Thief RiverFalls, Minn. Filed Mar. 2, 1960, Ser. No. 12,363 Claims. (Cl. 209-319)This invention relates to screening machines and in particular to thoseof the vibrating screen variety and more particularly to those of thetype which are moved or rocked in a circular or gyratory path to impartpositive rocking shifting movement to all parts of the screeningsurface.

In most of the screening devices of this type, the screening machinesand their supporting structures are subjected to unbalancing destructivevibratory shock which shortens the life of the machine and renders thesame very noisy in operation, particularly when they are operated athigh speeds which they normally must operate at to obtain the efiiciencyof screening desired. Because of this vibratory movement and destructiveunbalancing shock, it has previously been impossible in the past tomount the charging hoppers and the discharge funnels or spouts incompact communicating relationship with the screening box itself. In thescreening machines previously and presently available the screens tendto flex in the center due to their continuous circular motion at a highrate of speed which causes lost motion in the flexed portion of thescreen. Also, in prior art devices, the center of the screen isconventionally higher than the sides thereof and the material beingscreened therefor tends to run heavier in the sides than in the centercausing an uneven flow and screening of material as it passes throughthe screening devices.

Therefore, an important object of my invention is a novel screeningmachine in which the screening box or shoe is independently mounted andgyrated and which has the feed hopper and discharge spout mountedimmediately adjacent thereto in flow communication therewith withoutbeing subjected to the gyratory movement of the screening box or to anysubstantial vibratory movement resulting therefrom.

Still another object is a screening machine of the class describedhaving novel means for positively moving or rocking the screening box ina circular or gyratory path and which is balanced in such fashion thatthe destructive unbalancing vibratory shock normally associated withprior are devices is eliminated to provide a banced drive to reduce thenoise of operation and add to the life of the machine thereby providinga substantially noiseless vibrationless screener.

Still another object is a screening device of the class described havingnovel means for removably and releasably supporting and clamping thescreens in place to pre vent bending and bowing and flexing thereofduring use and also permitting easy removal of the screens for cleaning,repairing or replacing thereof.

Still another object is a screening machine of the class describedemploying novel screen bracing means which render the screens perfectlyflat during use enabling a uniform flow of material across the entirewidth of the screen.

Still another object is a screening machine of the class describedemploying novel screen clamping and supporting means which permit all ofthe screens to be clamped simultaneously by operation or actuation of asingle locking mechanism.

Still another object is a screening machine of the class describedhaving a novel screen supporting and bracing means which prevents lostmotion in the center of the screen when the screening shoe or box isgyrated through a generally circular movement about a generallyhorizontal transverse axis.

3,087,617. Patented Apr. 30, 1963 "ice Still another object is ascreening machine of the class described in which the screening box,feed hopper and discharge spout are compactly mounted on a common framein direct flow communication with one another and in which the screeningbox is gyrated without any vibratory motion being transferred to thehopper and the discharge spout.

Still another object is a screening machine for all types of screenablematerial having high capacity and adapted to prevent blinding orclogging of the machine and which eliminates the need for screenblinding brushes which are frequently required on many of the presentlyand previously available screening devices and those of the prior artand which is so designed as to reduce maintenance to a minimum.

Still another object is a screening machine of the class describedhaving a feed hopper with both positive control for bin feed operationand spring loaded control for mill stream operation.

Still another object is a screening machine of the class described whichfeatures bridge type construction employing light weight material andbridge type bracing providing tremendous strength with light weight toachieve a substantially vibrationless, noiseless machine.

Another object is a screening machine of the class described which isreadily disassembled and in which the screening box may be completelyremoved from the supporting frame to enable said box to be tipped ortilted so as to be passed through narrow doorways and the like and forconvenience in transportation thereof.

These and other objects and advantages of my invention will more fullyappear from the following description made in connection with theaccompanying drawings wherein like reference characters refer to thesame or similar parts throughout the several views, and in which:

FIG. 1 is a perspective view of the assembled screening machine of myinvention;

FIG. 2 is a side elevational View;

FIG. 3 is a front elevational view with portions thereof in brokensection;

FIG. 4 is a vertical longitudinal sectional view of the screening box;

FIG. 5 is a vertical transverse sectional view taken on the line 55 ofFIG. 2;

FIG. 6 is a detail side elevational view of the eccentric andcounterweight therefor;

FIG. 7 is a detail sectional view on an enlarged scale taken on the line7-7 of FIG. 5; and

FIG. 8 is a detail sectional view on an enlarged scale taken on the sameline as FIG. 7 and showing an alternate form of the invention.

Reference is now made to the accompanying drawings for a more detaileddescription of a preferred embodiment of my invention illustratedtherein. As best illustrated in FIGS. 1 and 2, the composite screeningmachine of my invention includes a screening box B, a feed hopper H anda multiple discharge manifold or spout S, all of which are mounted onand supported by a common main frame F, the side members of which aredetachably connected to the cross members thereof by the bolts 9 forfacilitating the assembly and disassembly thereof and complete removalfrom the screening box when desired.

Considering first the screening box B, it comprises a suitable shell orhousing 10 made of light weight sheet steel which is reinforced bysuitable transverse ribbing or channels 11 secured to the top of thehousing and by vertically disposed reinforcing members or channels 12disposed vertically on the sides of the housing. The housing isyieldingly and resiliently suspended in inclined fashion from front toback from the frame F by means of suitably tensioned helically coiledshock absorbers or springs 13 disposed adjacent the four corners of thehousing and interconnecting the housing with the frame. The lower endsof the springs 13 are connected With the screening box by means ofsuitable mounting brackets 13a secured to the outsideof the shell 10.The upper ends of the springs 13 are adjustably suspended from the frameF by means of a vertically disposed draw bolt 13b connected to the upperend of the spring, the draw bolt in turn being supported by a horizontalanchoring member 130 secured to the frame F and having an aperture inthe outer end thereof for receiving the draw bolt 13b. The tension inthe springs may be adjusted by vertically adjusting the draw bolt 13b.

The housing has enclosed therein a plurality of horizontally disposedscreens 14, and 16, the screens being of increasingly finer mesh as theyproceed from top to bottom, the topmost screen 14 being of coarser meshthan the next succeeding screen 15 and the bottommost screen 16 being ofthe finest mesh of all. Each of the screens are provided with inwardlyturned hook means or strips 1 7 on the sides thereof which are adaptedto be removably engaged by the downwardly extending clamps 18 providedon the inner sides of the housing to removably secure and mount thescreens inside the housing or box. The clamps 18 are resilient in natureand are each provided with a suitable transverse draw bolts 19 whichextend through the sides of the housing 10 and are threadedly engaged bythe T-handles 20 which extend outwardly from the sides of the housing10. By turning the T-handles, the draw bolts are thereby pulled againstthe clamps 18 which in turn press against the hook strips 17 with whichthey are engaged to stretch the screens and securely tighten the screensand hold them taut.

The bottom screen 16 rests on and is supported by a plurality oflongitudinal extending transversely spaced apart channel supportingmembers 21 (three are shown) which are secured to the bottom or floor ofthe housing 10. It will be noted that the channels 21 and the remainderof the screen supporting members hereinafter to be described arepreferably equi-spaced transversely or laterally from each other andfrom the sides of the housing 10 so that the lateral unsupported span ofthe screens between adjacent supporting members is substantially thesame. A spacing and clamping unit indicated generally by the letter Xrests on the top of the bottom screen 16 and extends vertically betweenthe screen 16 and the middle screen 15 immediately thereabove. Thesupporting and bracing unit X includes three transversely spacedsub-units each of which consist of a pair of vertically alignedlongitudinally extending clamping and supporting rods 22 which arerigidly interconnected to one another by suitable vertical bracingmembers 23, the sub-units in turn being laterally interconnected to oneanother and suitably braced by means of suitable horizontal transversebracing members 24. Thus, the lower rods 22 are adapted to rest upon thetop of the bottom screen 16 while the top rods 22 are adapted to engagethe under surface of the middle screen 15 which rests thereupon and issupported thereby. The supporting and bracing unit X is in turntightened and braced to prevent vibration and shifting thereof duringthe vibrating movement of the housing 10 by means of suitable tensioningcables 25 connected to the vertical bracing of the side sub-units andextending to and connecting with threaded adjustment draw bolts 26disposed in the sides of the housing 10.

A bracing and supporting unit Y similar to the previously describedsupporting and bracing unit X is disposed between the middle screen 15and the top screen 14 and includes sub-units consisting of thelongitudinally extending vertically spaced apart pairs of screenengaging and clamping rods 27 which are interconnected by suitablevertical bracing 28 and horizontal transverse bracing members 29,the.unit Y also being braced against shifting movement with respect tothe housing by means of tensioning cables 25 and tensioning bolts 26extending between the sides of the housing and the side sub-units ofunit Y. Thus, the lower rods 27 rest upon the top of the intermediatescreen 15 in direct opposition to the rods 22 engaging the opposite sideof the screen while the upper rods 27 engage and support the lower faceof the top screen 14 to support the same.

A hold down or clamping unit Z is disposed atop the top screen 14 andintermediate said screen and the roof of the housing 10. This unitincludes longitudinally disposed transversely spaced apart clamping rods30 which rest upon the top of the screen 14 directly opposite the rods27, which rods have mounted thereatop and rigidly secured theretolongitudinally spaced apart pairs of longitudinally disposed bowed orinverted V-shaped bracing members 31 interconnected by transverse rods31a each of the bows 31 having an upstanding guide arm 32 extendingupwardly from the mid-portion thereof, the upper end portion of whichprotrudes through an opening in the top of the housing 10. Each of theupstanding arms 32 carries thereon a helical coiled spring 33 freelywound thereabout and longitudinally compressible thereabout. The upperends of the springs 33 having bearing thereagainst suitable pressureapplying collars 34 which are freely slidable on the arms 32 and areadapted to be actuated for axial movement thereon by pivotalinterconnection with the outer end of the lower lever arm 35 of themultiple bell cranks indicated generally by the numeral C which bellcranks also include the transversely disposed pivotally mounted leversupporting sleeve 36 which is journalled in and rotatably supported bythe pairs of vertically spaced apart mounting flanges 37 found at eachside of the housing 10. Each of the sleeves 36 are provided with theupper lever arms 38 of the bell cranks, the front and back lever arms 38on the same side of the housing on each of the sleeves 36 beingactuatingly interconnected for simultaneous movement by means of ahandle bar link 39 which is pivotally connected at each end to saidfront and back lever arms 38.

The handle bars are actuated and the bell cranks rotated by means of atoggle unit on each side of the housing which includes a toggle handle40 which is pivotally mounted to a vertical upstanding flange 41 carriedby the top of the housing and mounted on a bearing 42 carried by theflange 41, the lower end of the handle 40 being pivotally connected tothe other half of the toggle unit consisting of the link or lever 43which is pivotally con nected to the toggle handle 40 at one end andpivotally connected to the back upper lever arms 38 of the bell cranks.Thus, by moving the handles 40 forwardly to the locked hold downposition shown in the drawings, the bell cranks are caused to rotate inthe opposite or clockwise direction thereby causing the collars 34 topress downwardly against the springs 33 which are compressed thereby andapply uniform pressure downwardly through the bowed braces 31 to theclamping rods 30 which in turn press downwardly to apply uniformpressure to the supporting and bracing units X and Y disposedtherebelow, thereby securely clamping the screens between theirrespective directly opposed clamping rods and maintaining them in aperfectly flat unfiexible condition, thereby preventing flexing of thescreens and lost motion during vibration or rocking of the screening boxand permitting uniform How of material through the entire width of eachof the screens. Thus, when the toggle is in locked condition, the topscreen 14 is securely clamped between the clamping rods 27 and 39, theintermediate screen 15 is clamped between the clamping rods 27 and 22and the bottom screen 16 is clamped between the rods 22 and the bottomchannel supports 21.

It will be noted that the channels 21 and the rods 22, 27 and 30 are invertical alignment with one another to enable the uniform application ofvertical downward pressure therebetween by means of the hold down unitand bell crank mechanism previously described.

It can be seen that the screens 14, 15 and 16 are firmly braced andsupported by the channel 21 and bracing units X and Y and hold down unitZ to keep them perfectly flat during use and prevent bowing and flexingthereof by means of the light weight but very sturdy and strong bracingand support previously above described. Thus, this arrangement not onlyprovides maximum strength with a minimum of weight but also provides thesupport and strength necessary to prevent the bending and flexing of thescreen and Without interfering with and positively promoting the uniformflow of material along the width of the screens. In addition, theclamping and supporting mechanism is easily operable as can be seen fromeither side of the machine by simple actuation of either of the togglehandles it), and the hold down arrangement also permits the screens tobe releasably and securely clamped in position so that they may beunclamped and easily removed for cleaning, repairing and/or replacingwhen necessary.

To positively move or rock the housing through a circular or gyratorypath, I provide a rotatable shaft 44 which extends through the entirebody of the screening shoe, the ends thereof being carried in ballbearings 45 secured directly to the frame. Ball bearings 46 are alsoprovided which are secured directly to the sides of the shoe or housing10 for mounting the screening box on the shaft. These bearings 46enclose and are engaged by eccentrics 47 carried by the rotatable shaft44. The shaft 44 represents the only direct positive connection betweenthe shoe or box B and the frame F of the machine. The shaft 44 alsocarries a cup-shaped fly wheel 48 which is secured thereto forsimultaneous rotary movement therewith, which fly wheel 48 is providedwith a balance weight or counterweight 49 installed on the inner thereofin direct radial alignment With the bearing unit and the shoe and itseccentric, which weight is 180 out of phase or timed 180 from eccentricin the shoe bearing. Therefore, While the shoe is exerting centrifugalforce in one direction, the counterweight is exerting an equalcentrifugal force in the directly opposite direction. Due to the factthat the counterweight 49 is centered directly in line with the bearings46 on the shoe :and the eccentrics 47, these centrifugal forces orstresses are applied to the shaft at the same point and therebyeliminates shaft whip and vibration from the frame and the box which isso prevalent in prior art devices and permits only positive balancedgyratory movement of the box B. The counterweight thus enables -theshaft and screening box to maintain positive balance at all times andresults in a substantially vibrationless and noiseless machine.

The shaft 44 is driven through any suitable transmission means such asthe drive pulley 57 and drive belt 58 by means of a conventional motor Mwhich is capable of rotating high speeds on the order of 1500 to 2000-rpm. Thus, due to the counterweight and counterbalance provided by thecounterweight 49 the shaft Whip associated with conventional types ofscreeners is thereby eliminated as well as vibration of the frame F.Therefore, due to the vibrationless frame F, it becomes possible toconnect the feed hopper 1-1 and discharge spout S directly to the framein direct flow communication with the screening box 13 without havingany substantial vibratory movement imparted thereto.

The hopper H shown is a funnel type hopper carried on the frame F bymeans of the outwardly extending portion 50 thereof. The lower dischargeend of the funnel or hopper H is provided with a feed chute 51 whichdisconnectedly overlaps the outer end of another feed plate chute 52connected in flow communication with the interior of the screeningmachine. The feed pipe delivering the prodnot or material to be screenedto the inlet mouth 59 of the hopper should preferably be positioned todeliver the material into the hopper from directly above or from frontor rear to accomplish uniform feeding of the screening box, sincefeeding from the side will cause uneven feeding thereof. The feed hopperis provided with positive control for bin feed operation. When operatingon mill stream, connecting links on each side of the hopper are replacedwith suitable adjustably tensioned springs which are hooked to the feedplate and adjusted to maintain enough product or material in the hopperto feed full width.

The multiple discharge spout S on the other or forward end of themachine is removably mounted on the front end of the frame F and inoverlapping disconnected relation with the forward ends of the screen-sto enable the various screening products to be separately removed anddisposed of. Thus, the multiple discharge spout S includes individualspouts 53, 54 and which are in independent flow communication with theirrespective screens, the outermost spout 53 handling the scalpings fromthe top screen 14, the middle screen 15 communicates with the middle ormain screen outlet 54 to remove the product passing over the screen 15and the third spout 55 is adapted to discharge the product passing overthe bottom screen 16. A discharge spout 56 is carried by the front endof the screening box and provides an outlet for the dirt and othermaterial which collects on the bottom or floor 10a of the screening box.

The screens hereinbefore described are substantially non-blinding in thescreening of dry granular materials. However, there are some types ofground oily-base products or materials which are subject to packingwhich are normally practically impossible to properly screen since theconventional brushing merely causes the oily product to mat the screen.Therefore, as an important part of this invention, I have developedmeans for preventing blinding of the screens by these oily materials,which means are best seen in FIGS. 5, 7 and 8. The novel means devisedcomprises laying one or more objects such as the metal chains 60 on topof and lengthwise of the screens 14, 15 and 16, which chains areanchored in any suitable fashion and are allowed to vibrate on top ofthe screens as they are gyrated, the vibration imparted to the screensby the chains preventing blinding by these oily materials. Rubbercovered chains may be substituted for the regular metallic ones wheredesired.

FIG. 8 illustrates a modification or alternate form of non-blindingmeans which consists of a series of rubber balls 61 interconnected withone another by flexible cord or cable means 62 to form an elongateflexible vibration imparting medium anchored to the housing in anysuitable fashion and adapted to rest atop :the screens in place of thechains 69, and repeatedly jar the screens during the gyration thereof tovibrate same and prevent blinding. Round bristle brushes may besubstituted for the rubber balls 61 where desired. These chains or theirequivalents may be adapted for detachable connection to the screener andapplied only when these oily materials and those subject to packing areto be handled thereby, if desired.

From the foregoing description, the advantages of my invention arereadily apparent. The entire screening mechanism, including thescreening box, hopper, discharge spout and frame are compactly united asa high capacity non-blinding unit which may be readily installed in aminimum amount of space close to the source of material to be screened.Because the unit is substantially noiseless and vibrationless, due tothe resilient yielding suspension of the screening box from the frameand balanced positive vibrationless gyratory movement thereof providedby the counterbalance eccentric drive shaft, the entire unit may bepermitted to rest freely on any suit-able supporting surface withoutbolting or otherwise permanently securing the unit thereto to enable theentire unit to be readily transported or moved from place to place asdesired, which is facilitated by the strong but light weightconstruction provided. The noiseless vibrationless features areparticularly attractive for obvious reasons. The easy-to-operate holddown arrangement for removably clamping the screens in place within thescreening box enables the screens to be readily removed and replacedfrom either end of the box and also enables the screens to be maintainedin a perfectly flat condition during use to permit uniform flow ofmaterial across the entire width of the screens and to prevent flexingof the screens and lost motion. The operation thereof is simplicityitself, requiring only two adjustments, that of the rate of the feed ofthe material and the speed of the motor, and maintenance is reduced to aminimum, since only the shaft, belt and four bearings bear watching andperiodic maintenance.

The novel, free floating nature of the screen clamping or hold downunits, together with the ease with which the screens may be slid intoand out of the screening box and the quickly releasable feature of thelocking or clamping mechanism are novel features which are not availableon prior art devices and materially add to the efficiency, usefulnes sand overall desirability for this type of screening device.

Thus, briefly, the screening machine herein disclosed and described hasthe following outstanding features which are distinct from and notavailable on other similar devices. These features are:

(1) The novel screen hold down system and the simple yet eflicient meansof operating same;

(2) The shaft counter balancing system employing a cup-shaped fly-wheelwith the counterweight disposed in direct radial alignment with thebearing unit and eccentric on the shoe;

(3) The light weight bridge-type construction;

(4) The ability to completely disassemble the machine and completelyremove the frame from the screening box to permit the equipment to passthrough narrow openings such as doorways and for ease in moving andtransportation; and

(5) The non-blinding chains or their equivalents for vibrating thescreens while they are being gyrated.

It will, of course, be understood that various changes may be made inthe form, details, arrangement and proportions of the various partswithout departing from the scope of my invention.

What I claim is:

1. In a screening machine, a screening box having a plurality ofremovable horizontally disposed vertically spaced screens, means forconnecting said screens to the sides of said box, means for drawing saidscreen's towards the sides of said box to stretch said screens andmaintain them in a taut condition, and means for supporting the medialportions of said screens to prevent flexing thereof and permit uniformflow of material across substantially the entire width thereof, saidmeans including a longitudinally disposed elongate member having thebottom screen resting thereon, spacing units interposed between adjacentpairs of screens, each unit including elongate longitudinally disposedvertically spaced and interconnected clamping members adapted to engageand press against the opposing sides of said adjacent screens, a holddown unit disposed above the top screen and including an elongatedlongitudinally disposed clamping member resting on the upper surface ofsaid top screen, all of said members being in substantial verticalalignment with one another from the top to the bottom of said box, andmeans for applying downward pressure against the hold down unit and itsclamping member to press the vertically aligned members together andsecurely clamp the screens therebetween to prevent flexing thereofduring use.

2. The structure set forth in claim 1, including bracing meansinterconnecting said spacing units and said box and preventing lateralmovement of said units.

3. The structure set forth in claim 2, wherein said means for applyingpressure against said hold down unit includes lever means pivotallymounted on said box, resilient means interconnecting said lever and saidhold down unit, and means for actuating said lever causing said lever tocompress said resilient means and apply downward clamping pressure tosaid hold down unit and said clamping members.

4. The structure set forth in claim 1, including a boxsupporting frame,means yieldingly and resiliently suspending the box from said frame, andmeans carried by said frame and cooperatively engaged with said box forcontinuously gyrating said box about a transverse horizontal axis toprovide positive balanced gyratory screening movement thereto.

5. In a screening machine, a screening box having a plurality ofremovable horizontally disposed vertically spaced screens, means forconnecting said screens to the sides of said box, means for drawing saidscreens towards the sides of said box to stretch said screens andmaintain them in a taut condition, and means for supporting the medialportion of said screens to prevent flexing thereof and permit uniformflow of material across substantially the entire width thereof, saidmeans including a longitudinally disposed elongate member having thebottom screen resting thereon, spacing units interposed between adjacentpairs of screens, each unit including elongate longitudinally disposedvertically spaced and interconnected clamping members adapted to engageand press against the opposing faces of said adjacent screens, a holddown unit disposed above the top screen and including an elongatelongitudinally disposed clamping member resting on the upper surface ofsaid top screen, all of said members being in substantial verticalalignment with one another from the top to the bottom of said box, andmeans for applying downward pressure against the hold down unit and itsclamping member to press the vertically aligned members together andsecurely, clamp the screens therebetween to prevent flexing thereofduring use, said last named means including a generally upwardlyextending guide arm carried by said hold down unit, a spring coiledabout said arm, the lower end of which is adapted to bear against saidhold down unit, a spring-compressing element slidably mounted on saidarm and adapted to bear against the upper end of said spring, a belltype lever pivotally mounted on said box, one lever arm of said bellcrank being pivotally connected to said spring compressing element toreciprocate the same towards and away from said spring, and toggle meansincluding an operating handle comprising one lever arm of the toggleinterconnected with the other lever arm of the bell crank and adapted toactuate same to selectively apply and release downward clamping pressureagainst the hold down unit through the spring and compressing elementcooperatively interconnected therewith.

6. Screening apparatus comprising in combination a screening unitincluding a screening box, a drive shaft extending transversely of saidbox and supporting same and freely rotatable relative thereto, eccentricmeans mounted on said shaft and cooperatively engaged with said box forgyrating said box about the axis of rotation of said shaft in responseto the rotation thereof, and structure for supporting said unitcomprising integral side frames and cross members extending between andinterconnecting said side frames, bearing means carried by each of saidside frames for receiving the outer ends of said drive shaft whereby thescreening unit is mounted on said supporting structure between the sidesthereof, said drive shaft being adapted for ready disengagement fromsaid bearings and the side frames being readily disconnectible from saidcross members whereby said side frames and the bearings carried therebycan be quickly detached from supporting engagement with said screeningunit to permit transportation of said unit independently of said sideframes.

7. A substantially vibrationless screening apparatus comprising incombination a screening unit consisting of a screening box, a pluralityof generally horizontally disposed, vertically spaced apart screensmounted within said box, means for drawing the screens towards the sidesof said box to stretch said screens and maintain them in taut condition,releasable clamping means adapted to grasp the screens intermediate thesides thereof and pre vent flexing thereof during use, a rotatable shaftextending through said box transversely thereof and freely rotatablerelative thereto, eccentric means mounted on said shaft for rotationtherewith and cooperatively engaged with said box and gyrating said boxabout the axis of rotation of said shaft, counterweight means mounted onsaid shaft in radial alignment with said eccentric and adapted to exerta force equal and directly opposite to that effected by said eccentricto prevent vibration of said shaft, supporting structure for saidscreening unit including integral side frames, second bearing meanscarried by said side frames adapted to receive and support the outerends of said drive shaft on said frames, cross members disposed adjacentthe feed and discharge ends of said box and extending between andinterconnecting said side frames, spring means resiliently suspendingsaid box from said structure, hopper means mounted on the cross memberadjacent the feed end of the box in disconnected flow communication withthe feed end of said box, spout means mounted on the cross memberadjacent the discharge end of the box in disconnected flow communicationwith the discharge end thereof, said shaft being quickly disengageablefrom said second bearing means and said side frames being adapted forquick disengagement from said cross members whereby the side frames andsecond bearing means can be quickly removed from supporting engagementwith said screening unit and whereby said screening unit can be readilytransported as an entirety independently of said side frames.

8. In a screening machine including a screening box and a supportingframe for said box, means for gyrating said box including a rotatableshaft carried by said box, bearing means carried by said 'box, andeccentric means cooperatively engaged with said shaft for rotationtherewith and rotatable within said bearing means to provide saidgy-ratory movement to said box in response to the rotation of saidshaft, a cup-shaped fly wheel mounted on said shaft and rotatabletherewith, said fly Wheel substantially enclosing said eccentric means,and counterweight means mounted on the peripheral rim of said fly wheelin direct radial alignment with said eccentric means and adapted toexert a force equal and diametrically opposite to that exerted by saideccentric means to eliminate whipping of said shaft.

9. In screening apparatus, a screening box and means for shaking same,said screening box including a plurality of generally horizontallydisposed vertically spaced screens, and means for engaging and holdingthe medial portions of said screens against flexing movement, said lastnamed means including means underlying and supporting a portion of thelowermost of said screens intermediate the sides thereof, spacing meansinterposed and extending between adjacent pairs of screens and engagingsame to maintain them a uniform distance apart, hold down means restingon the top of the uppermost of said screens, said supporting, spacingand hold down means being vertically aligned and adapted to cooperatewith each other to sandwich and clamp the screens therebetween and holdthem rigid, and means for squeezing said supporting, spacing and holddown means together simultaneously to accomplish the aforementionedclamping of said screens.

10. In screening apparatus including an elongate screening box, aplurality of generally horizontal screen means mounted in said box, andmeans for gyrating said box about a transverse horizontal axis, means:for releasably anchoring the side marginal edge portions of said screenmeans to said box, and releasable clamping means anchored to said box,said clamping means including elongate vertically aligned -clampingmembers disposed longitudinally of said box and adapted to engageopposite sides of the medial portion of said screen means intermediatethe marginal edge portions thereof and hold said screen means andprevent flexing thereof during gyration of said box, the opposingclamping members being capable of relative vertical opening and closingmovement therebetween for each screen, said clamping means includingmeans to cause simultaneous opening and closing movement of all of saidclamping members.

References Cited in the file of this patent UNITED STATES PATENTS440,301 Boorrnan Nov. 11, 1890 620,048 Oyer Feb. 21, 1899 1,534,416Schuler Apr. 21, 1925 1,693,940 Robins Apr. 12, 1927 1,713,143 OverstromMay 14, 1929 1,899,209 Petit Feb. 28, 1933 2,004,965 Wetlaufer June 18,1935 2,053,895 Burmeister Sept. 8, 1936 2,194,721 Piper Mar. 26, 19402,238,711 Soldan Apr. 15, 1941 2,246,483 Dillon June 17, 1941 2,358,453Gilson Sept. 19, 1944 2,477,123 Gil-son July 26, 1949 2,500,965 SymonsMar. 21, 1950 2,787,277 Barry Apr. 21, 1957 2,874,841 Peterson Feb. 24,1959 2,899,059 Schroth Aug. 11, 1959 2,964,186 Ferara Dec. 13, 1960

10. IN SCREENING APPARATUS INCLUDING AN ELONGATE SCREENING BOX, APLURALITY OF GENERALLY HORIZONTAL SCREEN MEANS MOUNTED IN SAID BOX, ANDMEANS FOR GYRATING SAID BOX ABOUT A TRANSVERSE HORIZONTAL AXIS, MEANSFOR RELEASABLY ANCHORING THE SIDE MARGINAL EDGE PORTIONS OF SAID SCREENMEANS TO SAID BOX, AND RELEASABLE CLAMPING MEANS ANCHORED TO SAID BOX,SAID CLAMPING MEANS INCLUDING ELONGATE VERTICALLY ALIGNED CLAMPINGMEMBERS DISPOSED LONGITUDINALLY OF SAID BOX AND ADAPTED TO ENGAGEOPPOSITE SIDES OF THE MEDIAL PORTION OF SAID SCREEN MEANS INTEMEDIATETHE MARGINAL EDGE PORTIONS THEREOF AND HOLD SAID SCREEN MEANS ANDPREVENT FLEXING THEREOF DURING GYRATION OF SAID BOX, THE OPPOSINGCLAMPING MEMBERS BEING CAPABLE OF RELATIVE VERTICAL OPENING AND CLOSINGMOVEMENT THEREBETWEEN FOR EACH SCREEN, SAID CLAMPING MEANS INCLUDINGMEANS TO CAUSE SIMULTANEOUS OPENING AND CLOSING MOVEMENT OF ALL OF SAIDCLAMPING MEMBERS.